Conventionally, an image processing apparatus such as a digital color copying machine, etc. aims at obtaining an output image faithful to an original image.
Therefore, a digital color copying machine performs each image processing in an image signal processing unit on digital input image data of an original image read by a scanner unit, visualizes the image-processed digital image data in a printer unit, and obtains a copied output closest possible to the original image.
In the image processing in the above mentioned image signal processing unit, the image data of red (R), green (G), and blue (B) read from the original image is converted into cyan (C), magenta (M), yellow (Y), and black (K) for color reproduction, and the printer unit forms an image on a recording paper based on the CMYK data.
A coefficient of each image processing in the image signal processing unit is set to an ideal value for appropriate reproduction of an original image read by a scanner unit into copied output by the printer unit.
However, an image is more or less deteriorated by image noise caused by the reading precision of the scanner unit, the color reproducibility of the printer unit, various factors in a data processing system, etc., thereby requiring means for correcting the image.
Especially, when a full-color image is reproduced, the unevenness in a even gray scale portion can be detected. Therefore, it is necessary to consider the smoothness as well as the resolution. However, if the resolution is emphasized, the even gray scale portion appears uneven, and the image looks unnatural. On the other hand, of the smoothness is emphasized, an edge portion and a character portion become blur, thereby reducing the resolution.
Therefore, the conventional color copying machine maintains the consistency between the resolution and the smoothness of an image in the following method.
First, image data in three colors R, G, and B obtained by reading an original image is checked on the edge/character portion and the even gray scale portion based on predetermined reference values by detecting an edge amount, determining the thickness of a fine line, etc. Then, an MTF (modulation transfer function) correction (spatial frequency correction) unit performs a predetermined edge emphasizing process on the image data of the edge/character portion, and performs a predetermined smoothing process on the image data of the even gray scale portion indicating a small change in gray scale to reproduce an image more clearly on the edge/character portion and more smoothly on the even gray scale portion. Thus, the deterioration of a reproduced image can be reduced while maintaining both resolution and smoothness.
However, in the above mentioned conventional color copying machine, it is desired that, for example, the level of the smoothing process can be varied depending on the type and pattern of image data to be processed in addition to switching between the above mentioned edge emphasizing process and the smoothing process with the development of high technology in function and image quality.
For example, in a photograph of a baby or a small child, it is desired that the image of his or her skin is to be more smoothly reproduced than other portions in the photograph. It is also desired that a photograph of woods is to be reproduced with the entire image smoothly, but with each leaf appearing clearly.
Therefore, to satisfy all these needs, it is suggested that a color copying machine is equipped with a determination circuit for recognizing the type or pattern of an image. In this case, however, there arises the problem that the circuit is costly, the determination computing process lowers the copying speed, etc.